Microwave sensor

ABSTRACT

“Actual correlation data” is stored at storage means 38A. Such “actual correlation data” is data representation(s) of correlation(s) between or among distance(s) to object(s) intended to be detected and phase difference(s) of respective reflected wave(s) established with due consideration having been given to reflection of microwave(s) by object(s) (ceiling surface(s), wall surface(s), floor surface(s), etc.) other than object(s) intended to be detected which may be present within area(s) intended to be protected. Distance(s) to object(s) intended to be detected is or are measured, based on such “actual correlation data,” from phase difference(s) of respective reflected wave(s) that has or have been detected.

TECHNICAL FIELD

[0001] The present invention relates to a microwave sensor (hereinafter“MW sensor”) which is an active sensor employing electromagnetic waveslower in frequency than visible light. In particular, the presentinvention relates to an improved MW sensor making use of a plurality ofmicrowaves of different frequency to detect object(s).

BACKGROUND ART

[0002] Conventionally known as one security device is an MW sensorwherein microwaves are transmitted toward protected area(s), and, in theevent that person(s) is or are present within protected area(s), wave(s)reflected from such person(s) (microwave(s) modulated due to the Dopplereffect) are received and person(s) (intruder(s)) is or are detected(e.g., Japanese Patent Application Publication Kokai No. H7-37176(1995)).

[0003] Moreover, also known as one type of MW sensor is a device whichemploys a plurality of microwaves of different frequency and which isconstituted so as to permit measurement of distance(s) to object(s). Inthis type of sensor, microwaves of, for example, two differentfrequencies are transmitted toward protected area(s), and phasedifference(s) between two IF signals based on respective reflected wavesis or are detected. Correlation(s) exist between or among such phasedifference(s) and distance(s) to target(s) (person(s) and/or other suchobject(s) intended to be detected), phase difference(s) tending toincrease with increasing distance(s) to target(s). In other words,distance(s) to target(s) can be measured by calculating such phasedifference(s). Below, operations for detection of phase difference(s)between/among IF signals in this type of sensor are described. Takingthe case where IF signals based on waves produced by reflection ofmicrowaves of two different frequencies are sinusoidal waves IFout1,IFout2 (having phase difference corresponding to distance to target) asshown at FIG. 3(a), rectangular waves A, B derived from these IF signalsmight respectively be as shown at FIG. 3(b). It will, moreover, bepossible to measure the distance to the target by detecting the phasedifference between these rectangular waves A, B (the phase difference Δtat the rising edge portion of the rectangular waves in the drawing).

[0004] However, where this type of sensor is installed indoors,measurement errors may occur due to influence of microwaves reflected byceiling surface(s), wall surface(s), and/or floor surface(s). Morespecifically, for targets present at the extreme near side of the sensorrange (e.g., on the order of 0 to 2 m) or targets present at locationsrelatively distant from the sensor (e.g., locations 8 m or more from thesensor), such measurement errors are small. However, for targets presentat locations other than the foregoing (e.g., locations on the order of 3to 7 m from the sensor), it is possible that measurement error will belarge. The reason this is the case is described below.

[0005] Referring to FIG. 4(a), description is first made with respect toa situation where the target is present at the extreme near side of thesensor range. Receiving antenna(s) for this type of sensor “a” arechosen such that directionality with respect to reception of reflectedwaves received from the front (reflected waves in horizontaldirection(s) which are directed toward the left in the drawing) is high;and conversely, such that directionality with respect to reception ofreflected waves from the side(s) and from regions thereabove andtherebelow (e.g., the reflected wave indicated by the alternating longand short chain line in the drawing) is low. For this reason, if target“b” is present at the extreme near side of the range of sensor “a”,microwaves from sensor “a” will directly irradiate target “b”, thesewill also be directly reflected therefrom onto sensor “a” (theirradiated wave and reflected wave indicated by solid lines in thedrawing; reflected waves received in such fashion being hereinafterreferred to as normally reflected waves), and received reflected wavesignal level will be high with respect thereto. In contrast thereto,received signal level will be extremely low for signals received atsensor “a” after reflection by ceiling surface “c”, floor surface “d”,and so forth as indicated by alternating long and short chain lines inthe drawing. For this reason, because the reflected waves forming the IFsignal for measurement of distance to target “b” are for the most partmade up of the normally reflected waves indicated by the solid lines inthe drawing, there is almost no occurrence of measurement error.

[0006] Referring to FIG. 4(b), description is next made with respect toa situation where target “b” is present at a location relatively distantfrom sensor “a”. In such a situation, where irradiated waves arereflected by ceiling surface “c” or the like as indicated by the dashedline in the drawing, or where reflected waves are reflected by floorsurface “d” or the like as indicated by the alternating long and shortchain line in the drawing, the path taken by microwaves will be longerthan the path taken by normally reflected waves (the path indicated bysolid lines in the drawing). However, because the distance to target “b”is large, it is possible to hold the difference between the foregoingpaths to a value at or below on the order of 10 percent as a fraction ofthe distance to this target “b”. For example, taking a case where target“b” is present at a distance of 10 m from sensor “a”, even if thedifference between the foregoing paths is as much as 1 m it will stillbe possible to hold the error to values at or below 10 percent. For thisreason, errors due to reflection of microwaves at ceiling surface “c”and floor surface “d” have almost no effect.

[0007] In contrast thereto, where, as shown at FIG. 4(c), target “b” islocated neither at the extreme near side of the range of sensor “a” norat a far distance from sensor “a”, reflected waves received at sensor“a” after reflection by floor surface “d” and so forth as indicated byalternating long and short chain lines in the drawing will be receivedfrom angles near the front of the antenna, and the received signal levelof such signals will be relatively high. Furthermore, where irradiatedwaves are reflected by ceiling surface “c” or the like as indicated bythe dashed line in the drawing or where reflected waves are reflected byfloor surface “d” or the like as indicated by the alternating long andshort chain line in the drawing, the path taken by microwaves is longerthan the path taken by normally reflected waves, and because thedistance from sensor “a” to target “b” is also relatively short it ispossible that the difference between the foregoing paths could be large(e.g., on the order of 50 percent) as a fraction of the distance fromthis sensor “a” to target “b”. In other words, reflected waves travelingvia paths much longer than paths of normally reflected waves arereceived at sensor “a” with relatively high received signal levels. Forthis reason, IF signals being formed from waves representingsuperposition of the foregoing normally reflected waves and reflectedwaves traveling via paths longer than paths of such normally reflectedwaves, measurement errors arising due to the influence of the latter,i.e., reflected waves (reflected waves traveling via paths longer thanpaths of normally reflected waves) will increase, greatly impairingreliability of sensor “a”.

[0008] Such problems are not limited to situations in which MW sensor(s)is or are installed indoors, but will also occur in similar fashionwhere MW sensor(s) is or are installed outdoors if object(s)constituting obstacle(s) is or are present within area(s) intended to beprotected and microwaves are reflected by such object(s).

DISCLOSURE OF INVENTION

[0009] The present invention was conceived in light of the such points,it being an object thereof to provide, in an MW sensor employing aplurality of microwaves of different frequency to detect object(s), anMW sensor of high reliability capable of accurately measuringlocation(s) (distance(s) from sensor(s)) of target(s) notwithstandingthe fact that such target(s) may be present at any location(s) withinarea(s) intended to be protected.

[0010] In order to achieve the foregoing object, the present inventionprepares, as actual correlation data, correlation(s) between or amongdistance(s) to object(s) intended to be detected and phase difference(s)of respective reflected waves, such correlation(s) being with respect toactual and not theoretical values of both, with consideration havingbeen given to reflection of respective microwave(s) irradiated fromsensor(s) by object(s) other than object(s) (target(s)) intended to bedetected, and carries out measurement of distance(s) to object(s)intended to be detected based on this actual correlation data.

[0011] More specifically, the present invention is predicated upon an MWsensor transmitting a plurality of microwaves of different frequencytoward area(s) intended to be protected, and, in the event thatobject(s) intended to be detected is or are present within the area(s)intended to be protected, receiving respective microwave(s) which is orare reflected and measuring distance(s) to object(s) intended to bedetected based on phase difference(s) between or among the reflectedwave(s). This MW sensor is equipped with storage means and measuringmeans. Storage means stores or store, in advance as actual correlationdata, correlation(s) between or among distance(s) to object(s) intendedto be detected and phase difference(s) of respective reflected wave(s)established with due consideration having been given to reflection ofmicrowave(s) by object(s) other than object(s) intended to be detectedwhich may be present within area(s) intended to be protected. Measuringmeans measures or measure distance(s) to object(s) intended to bedetected based on actual correlation data stored by such storage means.

[0012] In a specific example of installation of such an MW sensor,protected area(s) is or are space(s) within room(s); and object(s) otherthan object(s) intended to be detected are ceiling surface(s), wallsurface(s), and/or floor surface(s).

[0013] As a result of such specific features, notwithstanding the factthat microwaves transmitted from sensor(s) toward area(s) intended to beprotected may be reflected by object(s) (e.g., ceiling surface(s), wallsurface(s), and/or floor surface(s)) other than object(s) intended to bedetected and microwave path(s) may be longer than path(s) of theforegoing normally reflected wave(s), because the foregoing actualcorrelation data is prepared as data which takes into considerationportion(s) corresponding to such extension of path(s) due to reflection,it will be possible to obtain value(s) for distance(s) to object(s)intended to be detected as measured by sensor(s) that is or are inapproximate agreement with actual distance(s) to object(s) intended tobe detected. In other words, even where object(s) that could producereflected wave(s) other than normally reflected wave(s) is or arepresent within area(s) intended to be protected, it will nonetheless bepossible to accurately measure distance(s) to object(s) intended to bedetected and it will nonetheless be possible to achieve improved sensorreliability.

BRIEF DESCRIPTION OF DRAWINGS

[0014]FIG. 1 is a drawing showing circuit structure in an MW sensorassociated with an embodiment.

[0015]FIG. 2 is a drawing showing correlation between distance to targetintended to be detected and phase difference of respective reflectedwaves.

[0016]FIG. 3 is a drawing showing respective IF signals as well asrectangular waves which might be obtained therefrom in a conventionalexample.

[0017]FIG. 4 contains drawings for explaining conventional problem(s);(a) at same FIG. being a drawing showing a situation in which a targetis present at the extreme near side of the range of a sensor, (b) atsame FIG being a drawing showing a situation in which a target ispresent at a location relatively distant from a sensor, and (c) at sameFIG. being a drawing showing a situation in which a target is present ata location approximately midway between that of (a) at same FIG. andthat of (b) at same FIG.

BEST MODE OF CARRYING OUT INVENTION

[0018] Below, embodiments of the present invention are described withreference to the drawings. Here, description is carried out in terms ofa situation in which the present invention is applied to an MW sensorfor use as a security sensor, the MW sensor being such that microwavesof two different frequencies are employed for measurement of distance(s)to target(s) (intruder(s) or the like).

DESCRIPTION OF MW SENSOR CONSTITUTION

[0019]FIG. 1 shows circuit structure in MW sensor 1 associated with thepresent embodiment. As shown in the drawing, MW sensor 1 is equippedwith RF module(s) 2 and signal processing unit(s) 3.

[0020] RF module 2 is equipped with oscillator(s) 21 for generatingmicrowaves, modulator(s) 22 for changing frequency or frequencies ofmicrowaves generated by such oscillator(s) 21, transmitting antenna(s)23 for transmitting microwaves generated by oscillator(s) 21 towardprotected area(s), receiving antenna(s) 24 for receiving microwavesreflected by person(s) or other such object(s), and mixer(s) 25 formixing such received microwaves together with voltage waveform(s) fromoscillator(s) 21 before output thereof. That is, in the event that thereis or are person(s) or the like within protected area(s), microwavestransmitted toward protected area(s) from transmitting antenna(s) 23will, upon reflection by such person(s) or the like, be modulated infrequency or frequencies due to the Doppler effect before being receivedby receiving antenna(s) 24. After being received, such reflected wave(s)are at mixer(s) 25 mixed with voltage waveform(s) from oscillator(s) 21before being output as IF output signal(s) (IFout0) from RF module(s) 2to signal processing unit(s) 3.

[0021] Furthermore, signal processing unit 3 is equipped with firstoutput line(s) L1 and second output line(s) L2 respectivelycorresponding to each frequency of microwave transmitted fromtransmitting antenna(s) 23. Respective lines L1, L2 are equipped withpower supplies 31, 32, 33, IF amplifiers 34, 35, and comparators 36, 37;distance measuring arithmetic unit 38—which is characteristic of thepresent embodiment—being provided to the output side of comparators 36,37.

[0022] Respective IF amplifiers 34, 35 are connected to the output sideof RF module 2 by way of first switch SW1. First switch SW1 performsswitching so as to cause connection to first output line L1 when one ofthe aforementioned two varieties of microwaves is transmitted fromtransmitting antenna 23, and so as to cause connection to second outputline L2 when the other of the aforementioned two varieties of microwavesis transmitted from transmitting antenna 23. That is, the constitutionhere is such that IF output signal(s) (IFout1) associated with reflectedwave(s) produced by reflection from person(s) or the like duringtransmission of one of the aforementioned two varieties of microwaves isor are output to first output line L1, and IF output signal(s) (IFout2)associated with reflected wave(s) produced by reflection from person(s)or the like during transmission of the other of the aforementioned twovarieties of microwaves is or are output to second output line L2.

[0023] Furthermore, respective power supplies 31, 32 are connected tothe input side of RF module 2 by way of second switch SW2 which works inlinked fashion with the aforementioned first switch SW1. Switching ofthis second switch SW2 likewise causes connection to be made to eitherof respective power supplies 31, 32 depending on which of theaforementioned two varieties of microwaves is being transmitted fromtransmitting antenna 23. That is, the constitution here is such thatmodulator 22 is switched between two different microwave frequenciesdepending upon whether this second switch SW2 makes connection to theone power supply 31 or the other power supply 32, thus permitting thefrequency of the microwaves transmitted from transmitting antenna 23 tobe switched.

[0024] In accompaniment to switching operations occurring at respectiveswitches SW1, SW2, switching thus occurs at regular time intervals(e.g., every several ms) between first processing operations wherein oneof the aforementioned two varieties of microwaves is transmitted fromtransmitting antenna 23 toward protected area(s) and IF output signal(s)(IFout1) based on wave(s) produced by reflection thereof is or areoutput to first output line L1 of signal processing unit 3, with signalprocessing taking place at this first output line L1; and secondprocessing operations wherein the other of the aforementioned twovarieties of microwaves is transmitted from transmitting antenna 23toward protected area(s) and IF output signal(s) (IFout2) based onwave(s) produced by reflection thereof is or are output to second outputline L2 of signal processing unit 3, with signal processing taking placeat this second output line L2. In addition, during the respectiveprocessing operations, IF output signals output from RF module 2 areamplified by IF amplifiers 34, 35, the outputs from such IF amplifiers34, 35 being shaped into rectangular waves by comparators 36, 37 beforebeing output to distance measuring arithmetic unit 38.

[0025] Moreover, describing the aforementioned respective processingoperations in further detail, in the event that there is no person orthe like within protected area(s), because frequency or frequencies ofmicrowaves transmitted by transmitting antenna 23 will be equal tofrequency or frequencies of microwaves received by receiving antenna 24,the IF frequencies of the signals output from IF amplifiers 34, 35 willbe “0,” and no signal will be output from comparators 36, 37. Incontrast thereto, in the event that there is or are person(s) or othersuch object(s) within protected area(s), because microwaves received byreceiving antenna 24 will be modulated relative to frequency orfrequencies of microwaves transmitted by transmitting antenna 23, therewill be a change in the output signal waveforms from comparators 36, 37,the rectangular waves therefrom being output to distance measuringarithmetic unit 38.

DESCRIPTION OF DISTANCE MEASURING ARITHMETIC UNIT 38

[0026] Distance measuring arithmetic unit 38, which receives outputsignal waveforms from comparators 36, 37, will next be described. Thisdistance measuring arithmetic unit 38 receives output signal waveformsfrom the foregoing respective comparators 36, 37, measures distance(s)to object(s) (person(s)) intended to be detected based thereon, andoutputs results of measurement.

[0027] Distance measuring arithmetic unit 38 is provided with storagemeans 38A and measuring means 38B. Description of the respective meansfollows below.

[0028] Storage means 38A stores, in advance as “actual correlationdata,” correlation(s) between or among distance(s) to object(s) intendedto be detected and phase difference(s) of respective reflected wave(s)established with due consideration having been given to reflection ofmicrowave(s) by ceiling surface(s), wall surface(s), and floorsurface(s) constituting object(s) other than object(s) intended to bedetected which may be present within area(s) intended to be protected.This “actual correlation data” is data established taking into accountdegree(s) to which correlations between or among distance(s) toobject(s) intended to be detected and phase difference(s) of respectivereflected waves will be shifted from theoretical value(s) as a result ofreflection of microwave(s) by ceiling surface(s), wall surface(s), andfloor surface(s) when such MW sensor(s) 1 is or are installed in room(s)of typical size(s). For example, as shown in FIG. 2, distance to objectintended to be detected and phase difference of respective reflectedwaves are theoretically related after the fashion of a directproportion. In contrast thereto, actual correlation therebetween isactually displaced from theoretical values after the fashion of themeasured values shown in the drawing due to influence of microwavesreflected by ceiling surface(s), wall surface(s), and floor surface(s).Such real-life correlation is ascertained in advance throughexperimentation or the like, and this “actual correlation data(programmed line(s))” is or are stored in advance at storage means 38A.

[0029] Moreover, measuring means 38B measures distance(s) to object(s)intended to be detected based on “actual correlation data” stored by theforegoing storage means 38A. That is, phase difference betweenrespective rectangular waveforms output from the foregoing comparators36, 37 is determined, and the distance corresponding to this phasedifference is detected based on the foregoing “actual correlation data.”As a result, measurement of distance(s) to object(s) intended to bedetected with due consideration having been given to the influence ofreflection of microwaves by ceiling surface(s), wall surface(s), andfloor surface(s) is permitted. Taking the example shown in FIG. 2, ifthe phase difference between reflected waves (phase difference betweenIF output signals) is 60°, the theoretical value for the distance to anobject intended to be detected might be 5 m. However, this valueincludes an error due to the influence of reflection of microwaves byceiling surface(s) and/or the like. In the present embodiment, theactual distance to the object intended to be detected can be measured as3 m based on “actual correlation data” which takes into account theinfluence of reflection of microwaves by such ceiling surface(s) and/orthe like.

[0030] As described above, the present embodiment permits measurement ofdistance(s) to object(s) intended to be detected based on “actualcorrelation data” established with due consideration having been givento reflection of microwaves by ceiling surface(s), wall surface(s), andfloor surface(s). For this reason, notwithstanding the fact thatmicrowaves transmitted toward area(s) intended to be protected may bereflected by ceiling surface(s) and/or the like and microwave path(s)may be longer than path(s) of the foregoing normally reflected wave(s),because the foregoing “actual correlation data” is prepared as datawhich preemptively takes into consideration portion(s) corresponding tosuch extension of path(s) due to reflection, it will be possible toobtain value(s) for distance(s) to object(s) intended to be detected asmeasured by sensor(s) that is or are in approximate agreement withactual distance(s) to object(s) intended to be detected. It isconsequently possible to provide an MW sensor 1 of high reliability thatis capable of accurately measuring distance(s) to object(s) intended tobe detected.

OTHER EMBODIMENTS

[0031] The foregoing embodiment has been described in terms of an MWsensor 1 employing microwaves of two different frequencies to measuredistance(s) to object(s) intended to be detected. The present inventionis, however, not limited thereto, it being possible to employ microwavesof three or more different frequencies to measure distance(s) toobject(s) intended to be detected.

[0032] Furthermore, the foregoing embodiment was described in terms of asituation in which an MW sensor 1 is installed indoors. The presentinvention is, however, not limited to thereto, it being possible toapply the present invention to an MW sensor that is installed outdoors.In such case, the foregoing “actual correlation data” would be preparedas data taking into account reflection of microwaves by obstacle(s)and/or the like within outdoor area(s) intended to be protected.Furthermore, a constitution may be adopted in which a single MW sensoris furnished with both “actual correlation data” corresponding toindoors and “actual correlation data” corresponding to outdoors,operation of a switch or the like causing switching of the “actualcorrelation data” to be used for measurement operations. Moreover, wherefurnished with a plurality of sets of “actual correlation data,” aplurality of sets of “indoor actual correlation data” corresponding toindoor space sizes may be stored by storage means 38A and/or a pluralityof sets of “outdoor actual correlation data” corresponding toarrangements and/or the like of obstacle(s) and/or the like in outdoorspace(s) may be stored by storage means 38A.

[0033] Furthermore, MW sensor 1 of the present invention may be employedin applications other than security sensors.

Potential for Use in Industry

[0034] As described above, microwave sensor(s) in accordance with thepresent invention excel with respect to ability to accurately measurelocation(s) of object(s) intended to be detected notwithstanding thefact that such object(s) may be present at any location(s) withinarea(s) intended to be protected and may be effectively employed ashighly reliable MW sensor(s).

1. In the context of a microwave sensor transmitting a plurality ofmicrowaves of different frequency toward area(s) intended to beprotected, and, in the event that object(s) intended to be detected isor are present within the area(s) intended to be protected, receivingrespective microwave(s) which is or are reflected and measuringdistance(s) to object(s) intended to be detected based on phasedifference(s) between or among the reflected wave(s), a microwave sensorcharacterized in that it is equipped with: storage means storing, inadvance as actual correlation data, correlation(s) between or amongdistance(s) to object(s) intended to be detected and phase difference(s)of respective reflected wave(s) established with due considerationhaving been given to reflection of microwave(s) by object(s) other thanobject(s) intended to be detected which may be present within area(s)intended to be protected; and measuring means measuring distance(s) toobject(s) intended to be detected based on actual correlation datastored by the storage means.
 2. A microwave sensor according to claim 1characterized in that: protected area(s) is or are space(s) withinroom(s); and object(s) other than object(s) intended to be detected areceiling surface(s), wall surface(s), and/or floor surface(s).